Other NXP ProductsのトピックRF Amplifier input port DC part issue

RF Amplifier input port DC part issue

coyoo — Fri, 18 Jul 2025 03:45:20 GMT

Hello Guys

We are testing the RF Amp part in our application. The part number are BGA2851. Before the input signal is fed into BGA2851, one AC coupling capacitor inserted to cut the input signal's DC part. However, there always exists around 800mV level DC part when we measure BGA2851 input port thru oscilloscope. So we don't know why this can happen? and where does this DC part come from? As following image, the DC level is 840mV.

Re: RF Amplifier input port DC part issue

ErikaC — Fri, 18 Jul 2025 18:32:03 GMT

Hello,

The device internally sets a DC bias point at its input to ensure proper operation of the active transistor. While a coupling capacitor is used to block any DC component from your signal source, the amplifier itself applies a DC voltage at its input terminal.

This behavior is expected and should not pose any issue in normal operation.

Re: RF Amplifier input port DC part issue

coyoo — Mon, 21 Jul 2025 06:29:43 GMT

Hi ErikaC,

Thanks for you reply.

I have several questions need you help:

1. What's the internal bias DC level? Why datasheet does present this character?

2. Do this kind of RF amplifiers amplify the DC part of the input port? If so, in our case, the 840mV DC part will be amplifiered to 8400mV on output port. I thinks this is impossible.

3. BTW, do we need to install inductor after BGA2851's output port?